摘要:

AbstractA simple way to incorporate the solvent–peptide interaction in any available theory of the helix–coil transition is developed. The competition between the intramolecular hydrogen bonding and the solvent–polymer hydrogen bonding is considered in multi‐component solvents where some of the components have hydrogen‐bonding capacity. Molecular averages are computed by using the theory of Lifson and Roig. The experimental data of Yang are analyzed, and the range of acceptable values of the equilibrium constants of hydrogen bond formation is deduced. The enthalpy of the transition in multicomponent solvents is c

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe potentiometric titration of poly(L‐glutamic acid) was performed under conditions of varied ionic strength and concentration of added divalent cations. From these titration curves, the amount of divalent cations, especially magnesium, bound to poly(L‐glutamic acid) was determined using a new method of analysis based on polyelectrolyte theory. By comparison with the polyelectrolyte, poly(acrylic acid), it was found that there are no specific interactions between metal ion and poly(L‐glutamic acid) in either the helical or random coil conformation. The effect of these divalent cations on the conformation of poly(L‐glutamic acid) was also di

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe optical density–temperature profile of double‐stranded poly(A + U), triple stranded poly(A + 2U), and double‐stranded RNA from rice dwarf virus in solutions with and without poly‐L‐lysine has been examined. When poly‐L‐lysine is added, more than one melting temperatureTmis observed for poly(A + U) and poly(A + 2U). One of them is considered to correspond to the melting of the polynucleotide molecule free from poly‐L‐lysine, and another to the melting of a polynucleotide–poly‐L‐lysine complex. For rice dwarf virus RNA, theTmassignable to the complex is not found to be lower than 99°C. In every case, however, the hyperchromicity observed at theTmof the free poly‐nucleotide molecule is lowered linearly as the amount of poly‐L‐lysine added to the solution increases. This fact is taken as indicating that there is a stoichiometric complex formed. The stoichiometric ratio lysine/nucleotide in each complex is determined by examining the relation between the amount of poly‐L‐lysine added to the solution and the percentage of hyperchromicity remaining atTmof the free polynucleotide molecule. The ratio is found to be 2/3 for all of the three complexes. A discussion is given on the molecular conformations of four types of polynucleotide–polylysine complex hitherto found: (A) double‐stranded DNA plus poly‐L‐lysine in which the lyslne/nucleotide ratio is 1, (B) three‐stranded RNA [poly(A + 2U)] plus poly‐L‐lysine in which the ratio is 2/3, (C) double‐stranded RNA [poly (A + U) or rice dwarf virus RNA] plus poly‐L‐lysine in which the ratio is 2/3, and (D) double‐stranded RNA [p

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe one‐dimensional Ising model, with nearest neighbor correlation only, suitably modified, is used to explain the observed linear dependence of melting temperature of copolymeric DNA with GC content. Transition curves are plotted for regular, random, and Markoff distribution of base pairs for various values of a correlation parameterUbetween nearest neighbor bonds. Exact analytic formulas are given for fraction of bonds intact at a particular temperature for various regular distributions for allUand approximate ones for random and Markoff distributions for smallU. A scheme is indicated for further improvement. The model, in principle, makes it possible to estimate the statistical distribution of base pairs from the detailed shape of the transition curv

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractA survey has been made, by using computer methods, of the types of helices which polypeptide chains can form, taking into account steric requirements and intramolecular hydrogen‐bonding interactions. The influence on these two requirements, of small variations in the bond angles of the peptide residues, or of small changes in the overall dimensions of the helix (pitch and residues per turn), have been assessed for the special case of the α‐helix. Criteria for the formation of acceptable hydrogen bonds have also been applied to helices of other types, viz., the 3 10 −, γ−, ω−, and π‐helices. It was shown that the NH … O and H … OC angles in hydrogen bonds are sensitive to changes in either the NCαC′ bond angle or in the rotational angles about the NCαand CαC′ bonds. However, the variants of the α‐helix observed experimentally in myoglobin can all be constructed without distortion of the hydrogen bonds. For α‐helices, the steric and hydrogen bonding requirements are more easily fulfilled with an NCαC′ bond angle of 111°, rather than 109.5°. The decreased stability observed for the left‐handed α‐helix relative to the right‐handed one forL‐amino acids is due essentially only to interactions of the Cβatom of the side chains with atoms in adjacent peptide units in the backbone, and interactions with atoms in adjacent turns of the helical backbone are not significantly different in the two helices. Restrictions in the freedom of rotation of bulky side chains may have significant kinetic effects durin

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractS‐Carboxymethyl (SCM) kerateine preparations from a range of keratins were fractionated by acid precipitation into low‐sulfur (SCMKA) and high‐sulfur (SCMKB) fractions. Amiono acid analyses and optical rotatory dispersion measurements on the SCMKA fractions from different keratins indicated that the proportion of α‐helical material (30–64%) increased with increasing leucine and glutamic acid contents and decreased with increasing SCM‐cysteine and proline contents. It is shown that these variations in α‐helix contents are due mainly to differences in the conformations of the principal components of the SCMKA fractions, although there is also a smaller contribution arising from contamination with varying amounts of non helical components. The thiol + disulfide contents for the parent keratins were measured and compared with the SCM ‐cysteine contents of the solubilized fractions. In general the SCM‐cysteine contents of the SCMKA fractions increased with increasing thiol + disulfide content of the parent keratin, but these values were not directly proportional. The extent of total supercontraction in8MLiBr solution was measured for the parent keratins and shown to bear no significant relationship to their disulfide contents. From the extents of first‐stage and total supercontractions the disulfide contents of the contractile structures in the fibers were calculated according to a model described previously and compared with the analytical values for the SCM ‐cysteine contents of the SCMKA and SCMKB fraction. Data for both fractions were consistent with the model in that they were in each case related to the calculated values by a constant factor. However, because of simplifying assumptions in the model, it was not possible to identity positively one or other of these protein fractions with the contractil

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

摘要:

AbstractThe theory, character, and properties of cooperative transitions are developed with special reference to the abrupt changes of state which occur in protein solutions. Comparisons of helix–coil processes and protein conformational reactions show that though cooperation dominates both of these processes, there are important differences. Tests of two types for the validity of the two‐state approximation are presented with specific applications to proteins. Available experimental evidence demonstrates that the thermally induced reversible transitions of ribonuclease, α‐chymotrypsin, and chymotrypsinogen A under conditions thus far examined are two‐state p

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1966.360040811

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1966

数据来源: WILEY